There are two main systems for voluntary systems: "opt in" (anyone who has not given consent is not a donor) and "opt out" (anyone who has not refused is a donor). In some systems, family members may be required to give consent or refusal, or may veto a potential recovery even if the donor has consented. Opt-out legislative systems dramatically increase effective rates of consent for donation[2]. However, because of cultural and infrastructural factors, public policies and other factors, this does not translate directly into increased rates of donation.
Some countries with an opt-out system like Spain (34 donors per million inhabitants) or Austria (21 donors/million) have high donor rates and some countries with opt-in systems like Germany (16 donors/million) or Greece (six donors/million) have lower rates. However Sweden, which has an opt-out system, has a low rate as well (15 donors/million). The president of the Spanish National Transplant Organisation, has acknowledged Spain's legislative approach is likely not the primary reason for the country's success in increasing the donor rates, starting in the 1990s
